The present invention pertains to a navigation system and process for self-guiding unmanned industrial trucks with any desired wheel configuration, without a guide wire, and for free movement on paths and in curves along a virtual reference path. The path having at least one straight and/or curved section, wherein floor-installed discrete elements are provided which are in operative connection with the vehicle's internal control device via the vehicle's internal sensory analysis system.
It has been known for many years that the traffic lanes of unmanned industrial trucks can be marked by current-carrying wires in the traveled floor surface and that these wires can be inductively scanned by means of the vehicle's internal sensors or coils for finding the lane. This technology, called "industrial guiding", has a particular disadvantage that construction of the traveled sections requires expensive mechanical and electrical preparation of the floor, e.g., the milling of grooves, laying of wires, pouring out and grinding of the grooves, etc., in order to install the inductive lane loops in the floor surface. Fully aside from the often undesired damage to new shop floors which occurs in this connection, the time and cost involved are in many cases unacceptable.
Another method for guiding unmanned industrial trucks on predetermined guide paths is known as dead reckoning navigation. This consists in composing the paths of plurality of short, straight section elements which, when placed next to each other, represent a polygonal course. Steering is influenced such that each section element is traveled with the industrial truck having a defined steering angle through that section. By establishing a mathematical or trigonometric connection between the speed traveled s and the actual steering angle values .alpha., it is possible to calculate the change in the spatial position of the industrial truck. It has been clearly established that in practice there is an essential disadvantage to this principle of guiding. The calculation of the spatial position of the industrial truck is according to dead reckoning navigation, based on a starting point and the instantaneous position is subject to an inaccuracy which increases over the entire travel section. This is caused by a plurality of parameters that are not taken into account, e.g., unevennesses of the floor, vehicle tolerances, inexactitude of the angle and displacement measurements, etc. Since it is usually impossible in practice to accurately determine all the parameters which cause the error because of the costs and apparatuses which such measurements would require, free travel sections without guiding medium can be realized according to this principle of dead reckoning navigation only over short lengths ranging from 5 to a maximum of 10 m.
Experience showing that navigation along longer sections requires measurement of the ambient conditions is based on the above. In consideration of these relationships, distance sensors based on ultrasound or laser beams for scanning room walls or spatial distance marks, or optical sensors, for example, laser scanners, for scanning guide beams or bar codes arranged in space, have been suggested. These methods require that the actual measuring sections between the industrial truck and the room walls or the spatial marks be always free, and they must not be disturbed and consequently interrupted by persons, other vehicles, objects, or merchandise. Therefore, the conditions occurring in production and material handling facilities permit the use of this method in very few cases only.
The discovery that this disadvantage can be avoided by scanning floor marks was already taken into account in European Paten Application No. 0,193,985. It was suggested in this application that the floor serving as a travel surface be provided in the area of the traffic lanes with a geometric surface grid of marking elements which are scanned by means of a sensory analysis system arranged in the front part of the vehicle, and the values thus determined are trigonometrically linked for steering correction and guiding of the industrial truck. The relatively short grid distance between the individual marking elements, which approximately corresponds to the width of the vehicle, ensures independence of the path to be traveled from the geometric marking grid, as a result of which the path may extend in any preselectable pattern. However, the stationary floor installation of the marking points of the geometric surface grid, whose number may reach several hundred, depending on the existing space conditions and the length of the course to be traveled, represents an absolute maximum of expenditure in terms of means and cost, which is acceptable only in individual cases in which continuously varying travel courses are required. However, this undoubtedly represents an exception, because the trucks usually have to travel on fixed travel courses between existing production facilities and machines. Aside from this, due to the geometric surface pattern of the grid points needing absolutely equal distances between them, a pattern which is to be strictly maintained, and the absolutely perpendicular arrangement of the vertical and horizontal lines formed by the individual grid points in the surface, the floor installation of the marking elements requires utmost precision and care on the part of the installers. This is ultimately reflected in enormous costs.